1. Technical Field
The present teaching relates to method and system for analog circuit. More specifically, the present teaching relates to method and system for light emitting diode (LED) driver and circuits and systems incorporating the same.
2. Discussion of Technical Background
The usage of lighting devices in modern society is ubiquitous. Such lighting devices consume electricity. To save consumption of electricity, there have been various attempts to develop either lighting devices that consumes less electricity or control devices that can be used to adjust the brightness of the lighting, hence the level of usage of electricity, based on need. For example, LED lights has been developed that consumes much less electricity compared with other conventional lights. In addition, dimming devices have also been developed that can be operated to dynamically adjust the level of brightness. For instance, lighting in a bedroom of a home can be dimmed at night to save energy. However, dimming devices available today in the market place do not work well with LED lights due to the existence of resonance in an LED driver so that the dimming feature can become more of the problem rather than the solution.
For example, a triode alternating current (TRIAC) dimmer is a well known technology. However, a TRIAC dimmer requires a minimum holding current after being triggered. If the current drops below this level or becomes negative, the TRIAC dimmer will be turned off. The resonant nature of the input filter of a typical LED driver and the line inductance can easily lead to the reversal of the line current, which causes the TRIAC to lose conduction shortly after triggering of the TRIAC. In such situations, the TRIAC dimmer can enter into a chaotic operation state and the result is that the light is simply flickering rather than being dimmed.
FIG. 1 shows a typical TRIAC current waveform, which leads to the situation in which a TRIAC dimmer can be temporarily turned off when the TRIAC current goes below a minimally required level 150 due to the existence of resonance. As illustrated, when a TRIAC dimmer is triggered (turned on) at 100, the TRIAC current reaches a high level at 110. Before the TRIAC current eventually becomes stable shown at 140, the TRIAC current can fluctuate, due to resonance, e.g., to lower levels shown at 120 and 130. At 130, the TRIAC current level becomes lower than the minimally required level 150, and the TRIAC dimmer will be turned off until the TRIAC current goes back to a level higher than the threshold 150.
One typical conventional solution to this problem is to introduce a damping circuit, e.g., an RC-type or RCD-type of passive damping circuit to the resonant tank, to prevent the line current from going negative. FIG. 2 (Prior Art) shows such an RC-type damping circuit 260 employed in an LED circuit 220 to damp the existing resonance so as to prevent a TRIAC dimmer 215 from being temporarily turned off. This conventional solution includes a TRIAC dimmer 215 (212, 213, 217, and 218), which takes an AC input 205 and generates, by the trigger circuit 218, a triggering signal 210. The TRIAC dimmer 220 is connected with an LED driver 220 which is controlled by the TRIAC dimmer 220. The LED driver 220 comprises an input filter (225, 230, 235), a bridge rectifier (240, 245, 250, 255), a passive damping circuit 260 (including 265 and 270), a power converter 275, and a diode 280 that converts the output current to light.
There are a number of drawbacks associated with the passive damping circuit shown in FIG. 2 (Prior Art). This solution causes high power dissipation on the damping circuit itself, resulting in lower efficiency and a shorter lifetime due to higher temperature on the LED driver. Another drawback is that the capacitor 270 in the RC or RCD damping circuit 260 distorts the sinusoidal shape of the input current in a power factor correction (PFC) LED driver, thus, lowering the power factor.